Piezoelectric filter with different ratios of unpolarized vibration area to total vibration area in two filter elements

A piezoelectric filter comprising:

• a first energy-trapping dual-mode filter element including:
• a first piezoelectric substrate having first and second major surfaces;
• split electrodes provided on the first major surface;
• a common electrode which is provided on the second major surface and which faces the split electrodes;
• and
• terminal electrodes provided at or adjacent to edges of both of the first and the second major surfaces of the first piezoelectric substrate, each of the terminal electrodes being connected with one of the split electrodes and the common electrode;
• and
• a second energy-trapping dual-mode filter element including:
• a second piezoelectric substrate having first and second major surfaces;
• split electrodes provided on the first major surface;
• a common electrode which is provided on the second major surface and which faces the split electrodes;
• and
• terminal electrodes provided at or adjacent to edges of both the first and the second major surfaces, each of the terminal electrodes being connected with one of the split electrodes and the common electrode;
• wherein one of the split electrodes of said first filter element is interconnected with one of the split electrodes of said second filter element,
• wherein unpolarized sections are provided at edges of each of the first and second piezoelectric substrates, and said first and second filter elements each have a vibration region in which the energy-trapping vibration is generated, portions of each vibration region being located in the unpolarized sections, and
• wherein a ratio of the area of the portions of the vibration region which are located in the unpolarized sections of said first filter element to the area of the entire vibration region of said first filter element is different from a ratio of the area of the portions of the vibration region which are located in the unpolarized sections of said second filter element to the area of the entire vibration region of said second filter element.